Coating agent

Abstract

The present invention relates to a process for producing a coating substrate by applying at least one coating composition to the substrate and then curing it to give a coating film on the substrate, to the coated substrates obtained by this process, and to a coating composition.

We claim:— 
     
         1 . A process for producing a coated substrate by applying at least one coating composition to the substrate and then curing to obtain a coating film on the substrate, which comprises inducing and fixing in the coating composition a gradient in at least one chemical and/or physical property, substantially perpendicularly to the substrate surface.  
     
     
         2 . A process as claimed in  claim 1 , wherein the property attributing the gradient is selected from the crosslinking density, network arc length, network tension, microhardness, free volume, and combinations thereof.  
     
     
         3 . A process as claimed in either of claims  1  and  2 , wherein the gradient is induced during application of the coating composition to the substrate and fixed during cure.  
     
     
         4 . A process as claimed in either of claims  1  and  2 , wherein the gradient is induced after application of the coating composition to the substrate and fixed during cure.  
     
     
         5 . A process as claimed in either of claims  1  and  2 , wherein the gradient is induced and fixed during cure.  
     
     
         6 . A process as claimed in any of the preceding claims, wherein a coating composition is used which can be cured by at least two different mechanisms.  
     
     
         7 . A process as claimed in  claim 6 , wherein the coating composition can be cured with UV radiation and thermally.  
     
     
         8 . A process as claimed in  claim 7 , wherein the coating composition comprises 
 A) at least one compound containing at least two functional groups which are capable of reaction with a complementary functional group of a compound of component B) under conditions of thermal cure,    B) at least one compound containing at least two functional groups which are capable of reacting with a complementary functional group of a compound of component A) under conditions of thermal cure,    C) if desired, at least one compound having two C═C double bonds curable with UV radiation in the presence of a photoinitiator,    D) at least one photoinitiator,    E) if desired, at least one compound capable of forming free radicals thermally,    F) if desired, at least one reactive diluent, other than the compounds of components A) to C) which is capable of crosslinking under conditions of thermal cure,    G) if desired, at least one reactive diluent, other than the compounds of components A) to C) and F), which is capable of crosslinking with UV radiation,    H) if desired, nanoparticles,    I) at least one coating additive which is capable of inducing the gradient during cure, and    K) if desired, further customary coating additives other than compounds of component I),    with the proviso that at least one compound of components A) and/or B) additionally contains at least one UV-curable C═C double bond or the coating composition mandatorily includes at least one compound of component C).    
     
     
         9 . A process as claimed in  claim 8 , wherein component I) is selected from UV absorbers, colorless and colored pigments, and mixtures thereof.  
     
     
         10 . A process as claimed in either of claims  8  or  9 , wherein the coating composition contains component I) in an amount of at least 1% by weight, preferably at least 5% by weight, based on the overall amount of components A) to K).  
     
     
         11 . A process as claimed in any of the preceding claims, wherein the thickness of the coating film is at least 10 μm, preferably at least 20 μm.  
     
     
         12 . A coated substrate obtainable by a process as claimed in any of  claims 1  to  11 .  
     
     
         13 . A coating composition as defined in  claim 8 , containing components I) in an amount of at least 1% by weight, preferably at least 5% by weight.